Stiffi fuel cap vent / boil over ?

Ranger18

I had a stiffi gas cap vent on my old bike and now I put it on my 06 yz450f. I went riding this weekend and I knoticed that fuel was comming out of that little bastered. I have had this on for the last few rides without any problems, but this time fuel was everywhere. I'm thinking that it might have something to do with it being 110 degrees, but I'm not sure. Has anybody else experianced this.
I know most people are going to say "get rid of it", but I like it, if it is really the problem then I'll ditch it.
I don't think the fuel was boiling, because when I took the gas cap off, everything appeared to be fine.
Help